1. Field of the Invention
This invention relates to electrodynamic machines generally, and, more particularly to a novel stator winding configuration which permits operation of a two-phase A.C. motor in either of two speeds, while energizing all of the coils on the stator when operating at each speed. When applied to a generator, either of two frequencies may be produced when the generator is operated at a constant speed, using all of the coils on the stator.
2. Background Art
While the present invention is described as being applied to two-speed motors, it will be understood that it is useful as well when applied to A.C. generators to produce either of two frequencies when operated at a constant speed.
Two-speed A.C. motors of either the synchronous or the induction type have numerous applications, including use in refrigeration systems, motion control, fans, and other applications where a relatively large step change in speed is advantageous. Conventionally, the speed of such motors is changed by switching from one set of stator coils to another, with one set of coils energized to provide one speed and the other set of coils energized to provide the other speed.
In an A.C. motor, the minimum number of legs on the stator is equal to the number of stator magnetic poles times the number of phases. If one wished to have an A.C. motor with two nominal speeds of 1200 and 1800 rpm operated from a rwo-phase 60 Hz. power supply, it can be seen through the known relationship of speed =(120.times. frequency)/number of poles, where a "pole" comprises the number of adjacent legs having the same magnetization at a given time, that a 24-leg motor would be required, since the minimum number of legs for 1200 rpm operation is 12 and the minimum number of legs for 1800 rpm operation is 8, with the lowest number divisible by 12 and 8 being 24. The motor would be wound with one set of coils on every set of two adjacent legs for 1200 rpm operation and with a second set of coils on every set of three adjacent legs for 1800 rpm operation. Thus, a two-speed motor, two-phase motor of the conventional type would typically require 48 separate coils.
Accordingly, it is a principal object of the present invention to provide a two-speed A.C. motor which minimizes the number of stator legs required.
It is another object of the present invention to provide a two-speed A.C. motor in which all stator coils are energized at each speed.
Other objects of the present invention will, in part, be obvious and will, in part, be apparent from the following description.